The present invention relates to a power divider (transfer case) for a motor vehicle with a first and a second driven axle. Motor vehicles of this type (four-wheel drive vehicles) have assumed great importance in recent years.
What is especially important in four-wheel drive vehicles is the power divider which controls the power flux between the first and the second driven axle.
An input member of the power divider is in this case connectable to the output of a drive unit.
Such a drive unit of a motor vehicle has at least one engine. The engine may be an internal combustion engine, an electric motor, a hybrid motor or the like. The output of the engine is connected, as a rule, to a transmission. The transmission may be a multi-step transmission, such as a manual shift transmission, an automatic converter transmission, a double clutch transmission or else a continuously variable transmission, such as a CVT, toroidal transmission or the like.
The drive unit may be designed as a front drive unit or as a rear drive unit.
The power divider is installed, as a rule, in direct spatial assignment to the drive unit, that is to say, in the case of a front drive unit, in the region of the front axle and, in the case of a rear drive unit, in the region of the rear axle. In this case, for example, the power divider may also be integrated into a casing of the preceding transmission.
Where power dividers are concerned, a distinction is generally made between differential-controlled systems, clutch-controlled systems and mixed forms of these two systems.
Where differential-controlled systems are concerned, torque distribution to the two driven axles takes place by means of a longitudinal differential. This may be a bevel wheel differential or a planet wheel differential. In this case, generally, a specific ratio of torque distribution is predetermined, for example 50% front axle, 50% rear axle.
In clutch-control systems, only one axle is driven permanently. The second axle is cut in manually or automatically, as required.
Furthermore, in differential-control systems, it is possible to lock the differential completely or in a regulated manner, for example by means of a parallel-connected dog clutch or by means of a parallel-connected regulatable friction clutch.
DE 37 21 628 C2 discloses a power divider in which a longitudinal and a transverse differential are arranged coaxially with respect to the front axle of the motor vehicle. The transverse differential is arranged adjacently to a toothed ring which is in engagement with a driven gearwheel of a preceding multi-step transmission. The toothed ring is connected to the longitudinal differential via an outer hollow shaft. One output of the longitudinal differential is connected to an adjacent crown wheel which is in engagement with a cardan shaft for driving the rear wheels. The second output of the longitudinal differential is connected via an inner hollow shaft to the input of the transverse differential. A longitudinal lock in the form of a lamellar clutch is provided between the input of the transverse differential and a portion of the toothed ring.
Furthermore, an axle drive block with a differential lock is known from WO 02/28678 A1. Two planet wheel sets for forming a longitudinal and a transverse differential are coupled via a common ring wheel. The outer circumference of the latter comes into locking engagement with the inner circumference of the differential casing.